1. Field of Invention
The present invention relates to a color detecting sensor and a color detecting method. More specifically, the invention relates to a color detecting sensor and method for an ink ribbon to be used for a printer such as a thermal transfer printer utilizing a face sequential coating ink ribbon.
2. Related Art
A face sequential coating ink ribbon constituted by sequentially arranging ink coated faces having colors of cyan, magenta, yellow and black in a longitudinal direction is used for a printer such as a color thermal transfer printer. As a conventional color detecting sensor for detecting the color of the ink ribbon, for example, a black mark is given to a boundary between the colors of the ink ribbon and one light source such as an LED (light emitting diode) and two light receiving sensors such as photodiodes are provided with the ink ribbon interposed therebetween. The color detecting sensor detects the mark given to the ink ribbon through the light receiving sensor according to the delivery of the ink ribbon, thereby detecting the head of a delivery direction of each ink coated face and deciding the color based on the order of the ink coated face and a signal detected by the light receiving sensor.
Moreover, some other color detecting sensors for an ink ribbon according to the conventional example use two LEDs, that is, an LED having such a wavelength that light absorption for a first color of the ink ribbon having the four colors is the greatest and an LED having such a wavelength that light absorption for a third color is the greatest, thereby deciding a color based on a combination of detection signals corresponding to the two LEDs which are detected by the light receiving sensor. In this case, it is possible to detect the four colors of the ink ribbon without providing a mark for color detection on the ink ribbon.
In the case of an ink ribbon including an overprint layer for protecting a print face in addition to ink coated faces having the colors of cyan, magenta, yellow and black, however, there is a problem in that the color detecting sensors using the two conventional LEDs cannot distinguish the ink coated face having the color of yellow which can transmit red light, green light and infrared light very well from the overprint layer because the overprint layer is colorless and transparent.
On the other hand, there is a problem in that the area of the ribbon is increased to result in an increase in cost and waste of resources when a mark is given to the boundary between the colors of the ink ribbon.
Moreover, in the case in which the mark is not given to the ink ribbon, for example, only the ink coated face having the color of black is detected to specify the position of a head for each color based on a feed amount therefrom, it is necessary to provide a mechanism or sensor for accurately measuring the feed amount of the ink ribbon. Consequently, the device becomes complicated. Moreover, every time a power is turned on, it is necessary to excessively feed the ink ribbon to take the head position to be a reference. Therefore, there is a problem in that the resources are wasted and the cost is increased.
For example, in a conventional printer using an ink ribbon, in some cases in which the power of the printer is once turned OFF and is turned ON again, a different color from yellow (for example, a color prior to the yellow) is taken under a thermal head, for example, even if the yellow is detected on the color detecting sensor side. In some cases, moreover, the ink ribbon is excessively wound up so that a yellow portion for printing one screen (for example, a part corresponding to the size of a card) is not maintained, for example. In the conventional printer, therefore, it is necessary to provide a back tension coil on a delivery shaft, for example, and to reversely rotate a winding shaft, thereby rewinding the ink ribbon present under the thermal head up to the color detecting sensor and reconfirming the color when the color detecting sensor detects yellow during power-ON. However, the back tension coil has an original object to take up the slack. If the amount of rewinding is to be maintained to some extent irrespective of a change in a winding diameter, a back tension should also be increased. For this reason, a winding motor having a large size is required for winding up the ink ribbon against the back tension. Moreover, a tension applied to the ink ribbon is increased and there is a high possibility that the ribbon might be cut.
It is an object of the invention to provide a color detecting sensor and method for an ink ribbon which can detect a color, with an inexpensive and small-sized structure, also in an ink ribbon including a colorless and transparent portion such as an overprint layer.
In order to achieve the object, a first aspect of the invention is directed to a color detecting sensor for an ink ribbon comprising a first light emitting element for emitting red light, a second light emitting element for emitting green light, a third light emitting element for emitting blue light, a light receiving element for receiving light emitted from each of the first, second and third light emitting elements through the ink ribbon, and detecting means for detecting a color of the ink ribbon forming at least a colorless and transparent portion and the colorless and transparent portion based on an output signal of the light receiving element, the detecting means including a storage section for storing, as color reference data, the output signal of the light receiving element when the first, second and third light emitting elements emit light through the colorless and transparent portion respectively, and a color deciding section for comparing, with the color reference data, the output signal of the light receiving element when the first, second and third light emitting elements emit light through the color formed on the ink ribbon respectively, thereby deciding the color of the ink ribbon.
Accordingly, the color reference data are acquired and compared with the output signal measured through the color formed on the ink ribbon. Consequently, it is possible to decide the corresponding color of the ink ribbon based on the characteristic of the output signal for each of the red light, the green light and the blue light.
Moreover, a second aspect of the invention is directed to the color detecting sensor for an ink ribbon according to the first aspect of the invention, wherein the ink ribbon has five kinds of colors of yellow, magenta, cyan, black and a colorless portion.
Accordingly, even if a special mark is not given to the ink ribbon, the colorless portion and yellow can be distinguished from each other. Thus, it is possible to constitute an ink ribbon capable of carrying out printing well.
Furthermore, a third aspect of the invention is directed to a color detecting method for an ink ribbon comprising a first light emitting element for emitting red light, a second light emitting element for emitting green light, a third light emitting element for emitting blue light, a light receiving element for receiving light emitted from each of the first, second and third light emitting elements through the ink ribbon, and detecting means for detecting a color of the ink ribbon forming at least a colorless and transparent portion and the colorless and transparent portion based on an output signal of the light receiving element, the detecting means serving to store, as color reference data, the output signal of the light receiving element when the first, second and third light emitting elements emit light through the colorless and transparent portion respectively, and to compare, with the color reference data, the output signal of the light receiving element when the first, second and third light emitting elements emit light through the color formed on the ink ribbon respectively, thereby deciding the color of the ink ribbon.
Accordingly, the color reference data are acquired and compared with the output signal measured through the color formed on the ink ribbon. Consequently, it is possible to decide the corresponding color of the ink ribbon based on the characteristic of the output signal for each of the red light, the green light and the blue light.
Moreover, a fourth aspect of the invention is directed to the color detecting sensor for an ink ribbon according to the first or second aspect of the invention, wherein the light receiving element is provided on this side for one color of the ink ribbon from a head portion for transferring the ink ribbon to a medium.
Furthermore, a seventh aspect of the invention is directed to the color detecting method for an ink ribbon according to the third aspect of the invention, wherein the light receiving element is provided on this side for one color of the ink ribbon from a head portion for transferring the ink ribbon to a medium and serves to detect a boundary of colors of the ink ribbon on this side for one color of the ink ribbon from the head portion.
Accordingly, the color of the ink ribbon can be detected on this side for one color of the ink ribbon from the head portion. The case in which the color of the ink ribbon which is detected through the color detecting sensor is changed implies that the boundary of the colors of the ink ribbon passes through the light receiving element on this side for one color of the ink ribbon from the head portion. On the other hand, when the boundary of the colors of the ink ribbon is positioned on the light receiving element on this side for one color of the ink ribbon from the head portion, the start position of the color of the ink ribbon is set in the position of the head portion. In other words, the boundary of the colors of the ink ribbon is detected on this side for one color of the ink ribbon from the head portion so that the start position of the color of the ink ribbon can be aligned with the head portion.
More specifically, a fifth aspect of the invention is directed to the color detecting sensor for an ink ribbon according to the fourth aspect of the invention, wherein at least two light receiving elements are provided and serve to detect at least two colors constituting a boundary of the colors of the ink ribbon on this side for one color of the ink ribbon from the head portion.
Furthermore, an eighth aspect of the invention is directed to the color detecting method for an ink ribbon according to the seventh aspect of the invention, wherein at least two light receiving elements are provided and serve to detect at least two colors constituting a boundary of the colors of the ink ribbon on this side for one color of the ink ribbon from the head portion.
Accordingly, in the case in which at least two colors are detected by at least two light receiving elements, the boundary of the colors of the ink ribbon is present on this side for one color of the ink ribbon from the head portion and the start position of the color of the ink ribbon is set in the position of the head portion. In other words, when at least two light receiving elements detect different colors based on the positional relationship between the head portion and at least two light receiving elements, the color detected by the light receiving element on the side closer to the head portion is surely present under the head portion, and furthermore, a length required for printing can be maintained. Moreover, at least two light receiving elements are used. Consequently, it is possible to detect the boundary of the colors of the ink ribbon on this side for one color of the ink ribbon from the head portion even if the ink ribbon is stationary.
Moreover, a sixth aspect of the invention is directed to a color detecting sensor for an ink ribbon, wherein at least two color detecting sections for detecting a color of the ink ribbon are provided and serve to detect at least two colors constituting a boundary of the colors of the ink ribbon on this side for one color of the ink ribbon from a head portion for transferring the ink ribbon to a medium.
Furthermore, a ninth aspect of the invention is directed to a color detecting method for an ink ribbon, comprising the steps of detecting at least two colors constituting a boundary of colors of the ink ribbon on this side for one color of the ink ribbon from a head portion for transferring the ink ribbon to a medium and aligning a start position of the color of the ink ribbon with the head portion.
Accordingly, in the case in which at least two colors of the ink ribbon are detected on this side for one color of the ink ribbon from the head portion, the boundary of the colors of the ink ribbon is provided on this side for one color of the ink ribbon from the head portion. At the same time, the start position of any of the detected colors on the side closer to the head portion is set in the position of the head portion. In other words, the boundary of the colors of the ink ribbon is detected on this side for one color of the ink ribbon from the head portion. Consequently, the start position of the color of the ink ribbon can be aligned with the head portion.